This invention relates generally to determining position by electromagnetic radiation. More particularly, the invention relates to an improved system for determining a time period in which to make initial contact with a communications system based on the position of the user.
As the world becomes a more crowded and busy place, the use of radio bandwidth has correspondingly become more crowded. Furthermore, more devices in the hands of more people attempt to make contact with a variety of communication services such as cell phones and satellite uplinked communication services. This has resulted in the increased likelihood of "collisions", that is, several individuals attempt to establish initial contact with a service at the same time. While a need has been recognized to manage the increased traffic levels in a more efficient manner to allow the greatest use of the available bandwidth, most of these schemes are available only once the initial contact has been made with the service. Until service has been established, and bandwidth assigned to the user, each device must continually request service until recognized. As one can imagine, the repetitious requests for service further constrain the already crowded bandwidth and diminish the likelihood that any one request will be immediately fulfilled by the communication service.
The inventors propose a system in which the time slot in which the initial contact with a communication service is governed by the user's position. The Global Positioning System (GPS) is currently the most precise positioning system generally available to the general public and has significantly dropped in price in recent years. The GPS comprises a network of 24 satellites orbiting the earth. Each satellite transmits a ranging signal modulated on a 1.575 Ghz carrier. By monitoring the signal from a plurality of satellites, a GPS receiver can determine its position, i.e. latitude, longitude and altitude, to an accuracy of about 15-100 meters. In general, a GPS receiver can accurately determine its position if signals from three or four of the GPS satellites can be received. More accurate signals are available to the military. Differential GPS, also available to the public, is more accurate than standard GPS, but requires an additional land based transmitter and special permission from the government.
Many of the uses for GPS-based systems proposed are in the realm of mapping or collision avoidance applications. Notably one such GPS-based system is taught by "Traffic Alert and Collision Avoidance Coding System", U.S. Pat. No. 5,636,123 to Rich et al. In the Rich system, the airspace is divided up into a grid of volume elements. A collision avoidance signal is transmitted wherein the carrier signal is modulated by a psuedonoise code which is function of the volume element in which the aircraft is located. Each aircraft only tracks collision avoidance signals from vehicles in its own and immediate surrounding cells. Based on the calculated paths of the aircraft, a warning of an impending collision can be provided to the pilot.
The Applicants have proposed an improved tracking and collision avoidance system in "Time Multiplexed Global Positioning System Cell Location Beam System" Ser. No. 09/239,335, Attorney Docket No. AT9-98-870 filed the same day as the present application, is commonly assigned and is hereby incorporated by reference. Although the invention described in the incorporated application does not address the problems of reducing radio traffic and improving the likelihood that an initial contact with a communication service will be successful, it does share an overall cell structure with the present invention.
This invention solves these and other important problems.